This R21 application was prepared in response to the RFA entitled Epigenomic Modifications in Neurodevelopment. As described in the RFA, our studies are broadly designed to characterize epigenetic events involved in neurodevelopmental processes and to identify epigenome-wide marks associated with vulnerability to mental disorders. The proposed studies will address cell specificity in the brain across development, and focus on how several epigenetic modifications contribute to the development and maturation of a defined population of brain cells known as the locus coeruleus noradrenergic neurons (LCNN). LCNN constitute a critical component of the circuitry that is necessary for the processes of learning, memory, attention, sleep, arousal, anxiety, and responses to stress. Abnormalities of the LCNN are thought to contribute to the symptoms of attention deficit hyperactivity disorder, depression, Parkinson's and Alzheimer's diseases, and sleep disorders. Our studies focus on the key periods of development of LCNN from the completion of neurogenesis in the fetus through postnatal maturation and the establishment of functional synaptic connections, and conclude with adulthood in both male and female subjects. We have developed a method to purify defined neuronal populations throughout lifespan by fluorescence-activated cell sorting using transgenic mice that express enhanced green fluorescent protein (EGFP) under the control of the regulatory elements of genes expressed exclusively in these populations. In this study we will use transgenic mice (designated Dbh- EGFP) that express EGFP under the control of the regulatory elements of the dopamine 2-hydroxylase (Dbh) gene - a marker of noradrenergic neurons. By combining several state-of-the-art experimental approaches, we will generate the first comprehensive characterization of the genome-wide developmental pattern of the LCNN transcriptome [for both messenger RNA (mRNA) and microRNA (miRNA)], the DNA CpG methylome, and genome-wide maps of methylated histone H3 (e.g. H3K4me1, H3K4me2, H3K4me3, H3K9me3, H3K27me3). We will integrate this novel information into a framework defined by chromatin state maps and developmental gene expression profiles of LCNN. We will develop interactive bioinformatics tools designed to manage, visualize and integrate these data. This study, supported by an R21 mechanism that focuses on a single population of neurons highly relevant to mental health (the LCNN), will serve as a proof of concept for our long- term goal: to establish a comprehensive atlas of developmental epigenomic events that occur in key neuronal populations purified from specific brain regions and identified by their neurotransmitter (e.g. GABA, dopamine, serotonin, acetylcholine) or neuropeptide (e.g. galanin, NPY, VIP, substance P) phenotype. A large collection of the relevant EGFP-expressing transgenic mouse lines has been generated and is available at the NIH- supported GENSAT resource.